1. Field of the Invention
The invention relates to a complementary metal oxide semiconductor (CMOS) image sensor and a method of operating the same and, more particularly, to a CMOS image sensor and a method of operating the same capable of improving fabrication yield rate through self-calibration.
2. Description of the Prior Art
Since image sensors have been developed well and image processing speed has been improved, people have paid much attention to optical touch screen. So far the image sensor is divided into a charge coupled device (CCD) image sensor and CMOS image sensor. In general, the CCD image sensor has less noise and better image quality than the CMOS sensor. However, signal processing circuits of the CMOS image sensor can be integrated into single chip so as to minimize electronic device. Furthermore, the CMOS image sensor has lower power consumption than the CCD image sensor, so it has become more and more popularly.
Referring to FIG. 1, FIG. 1 is a schematic diagram illustrating an optical touch screen 1 of the prior art. As shown in FIG. 1, the optical touch screen 1 comprises a touch panel 10 and two CMOS image sensors 12 and 14. The CMOS image sensors 12 and 14 are respectively disposed at both sides of the touch panel 10. When a user uses an object 16, such as finger, stylus, or the like, to operate the touch panel 10, the CMOS image sensors 12 and 14 will sense a projection of the object 16. Afterward, if an angle between the projection and the touch position is known and a distance between the two CMOS image sensors 12 and 14 can be obtained, a coordinate of the touch position can be then calculated.
Referring to FIGS. 2 and 3, FIG. 2 is a schematic diagram illustrating a moving trajectory 160 of the object 16 projected on the CMOS image sensor 12 shown in FIG. 1, and FIG. 3 is a schematic diagram illustrating a moving trajectory 160′ of the object 16 projected on the CMOS image sensor 12 shown in FIG. 1. For example, if the CMOS image sensor 12 is attached to the touch panel 10 without deviation or obliqueness, the moving trajectory 160 of the object 16, which is projected on a pixel array unit 120 of the CMOS image sensor 12, has a rectangular shape, as shown in FIG. 2. However, if the CMOS image sensor 12 is attached to the touch panel 10 with deviation or obliqueness due to assembly tolerance, the moving trajectory 160′ of the object 16, which is projected on the pixel array unit 120 of the CMOS image sensor 12, has an oblique shape, as shown in FIG. 3. If the moving trajectory 160′ of the object 16 is oblique, the read-out circuit 122 needs to read more pixel data for following algorithm so as to eliminate the influence of assembly tolerance. Consequently, operating frequency and power consumption of the system will increase a lot.